There is a major need for peristaltic pumps the tubes of which will last longer than those of prior-art peristaltic pumps. Various tube materials have been employed in an effort to increase tube life and achieve other benefits, but despite such materials the problem of wear continues to be a major one.
It is conventional in peristaltic pumps to flatten or "pinch" tube walls against a surface. The relationships between the parts may be such that the tube is partially occluded, fully occluded, or over occluded. Flexural fatigue occurs where the tube is repeatedly creased, and this and other factors cause spallation of the inner surface of the tube. Shedding of tube particles from the inner wall of the tube is a problem not only because of decreased tube life, but because the interior size of the tube can be caused to vary in an irregular manner--thus creating changed and/or unpredictable flow rates. The repeated creasing of the tube, as it is flattened against a back-up surface, can also cause cracking of the tube, or permanent deformation thereof with consequent diminished flow rate.
It is important that an apparatus and method be provided by which the tendencies toward fatigue, spallation, cracking, permanent deformation, and variations in flow rate are minimized. It is also important that this be achieved in a simple and effective manner having no major effect on the cost of the peristaltic pump or meter.
Relative to another aspect of the invention, it is desired to provide an extremely simple peristaltic pump that in many instances does not require gearing, and does not require complex components. It is also desired that the simple and economical arrangement of parts be such that fluid may be pumped or metered in opposite directions simultaneously, and with minimized creep or crawl of the tubes.